PNA versus VNA. Which kind of them measure X parameter

What is the basic difference of PNA and VNA?

I want to measure X parameter of power transistor. Can all the PNAs do these measurments?

No..VNA=Vector Network Analyzer(It's a Common Name)
PNA is a model/series of Agilent VNAs.Some models are capable to measure X-Parameters, some are not.
For more information look at Agilent website.

Thank you for your kindly response
how can i understand which pna measure x-parameter? is it written in the pna data sheet?
I want to measure x-parameter, is it necessary to have some option on pan? if yes, which options?

PNA-X series are capable to measure x-parameters.More info
http://www.home.agilent.com/en/pc-10...0&cc=FR&lc=fre

Could you please describe me the difference between VNA and PNA and PNA-L network analyser?
thanks